Ok, ok, corny as hell, I know, but this one made me laugh this morning.

Herbert A. Millington
Chair – Search Committee
412A Clarkson Hall, Whitson University
College Hill, MA 34109

Dear Professor Millington,

Thank you for your letter of March 16. After careful consideration, I regret to inform you that I am unable to accept your refusal to offer me an assistant professor position in your department.

This year I have been particularly fortunate in receiving an unusually large number of rejection letters. With such a varied and promising field of candidates, it is impossible for me to accept all refusals.

Despite Whitson’s outstanding qualifications and previous experience in rejecting applicants, I find that your rejection does not meet my needs at this time. Therefore, I will assume the position of assistant professor in your department this August. I look forward to seeing you then.
Best of luck in rejecting future applicants.
Sincerely,
Chris L. Jensen

As did this one:

Treated like family